In recent years, recording media such as CD, LD, MD, 3.5" data files, 5.25" data files and PD have achieved practical use as a recording medium for optical information, acoustical information, or computer data and the like. In the course of our progress towards information society, an optical recording/reading medium that combines high density, high capacity, and high speed is in demand. In this respect, a magneto-optical recording medium with a magnetic induction type super resolution technique has caught attention as a technique that exceeds the resolution of a light beam, and is expected to become a core technology for future high density optical recording media. Suggestions concerning this matter can be found in the Publication of Unexamined Patent Application Nr. Hei 03-242845 among others. Furthermore, it has been suggested to achieve an even higher density for recording/reading, through combined use of the super resolution technique and a magnetic modulation recording technique, which allows easy recording of micro-marks. Publication of Unexamined Patent Application Nr. Hei 03-242845 also makes suggestions concerning this matter.
Referring to FIG. 19, an example of a prior art super resolution technique is explained below. First of all, the information is recorded using a known recording technique, such as light modulation or magnetic modulation. The recorded information is stored in a recording layer 7. When the information is read, the recording medium moves in arrow direction A. Preceding the reading, the magnetization of a reading layer 5 is already oriented in one direction by an initializing magnetic impression means 8. A reading beam is focused, and an irradiation domain 1 is irradiated. Together with the reading beam irradiation, the reading layer 5 is heated. When the temperature rises due to the heating, the exchange coupling force acting in the recording layer 7 and the reading layer 5 grows stronger, and a magnetic domain recorded in the recording layer 7 is transcribed into the reading layer 5 via an intermediate layer 6. Moreover, in the high temperature domain, the intermediate layer 6 exceeds the Curie point, the magnetic coupling between the recording layer 7 and the reading layer 5 is interrupted, and the magnetization of the reading layer 5 is oriented into one direction by a reading magnetic field impression means 9. In other words, in the beam irradiation domain 1, a low temperature mask domain 2 and a high temperature mask domain 3 become the masked state in order to orient the magnetization into a fixed direction unaffected by the recorded information. Hence, when the information is read, the magnetic domains of the recording layer 7 are transcribed into the reading layer 5 in an aperture domain 4 only. Consequently, it is possible to enlarge considerably the resolution, which was previously determined by the size of the light beam irradiation domain 1.
In order to improve the high resolution performance as an effect of this super resolution reading technique even further, a joint use of magnetic modulation, allowing an easy recording at higher density, has been suggested. Publication of Unexamined Patent Application Nr. Hei 03-242845 makes suggestions concerning such matter.
However, the above configuration has posed several problems, which shall be described below.
(1) When the magnetization of the aperture domain 4 of the reading layer 5 is reversed according to the magnetization of the recording layer 7, the translation of the magnetic domain wall is not that fast. For that reason, although the magnetization of the aperture domain 4 of the reading layer 5 reverses quickly in the direction of the magnetic field that is impressed by the reading magnetic field impression means 9, the reversal in the other direction becomes slow. Not only does this lead to a distortion of the reading wave form, but it also enlarges the edge shift for a mark edge recording with a higher density recording. Furthermore, if the linear velocity is raised to accelerate the transfer rate, this drawback becomes even more severe. Consequently, this poses an obstacle on the way to higher density and higher transfer rate.
(2) To initialize the magnetization of the reading layer 5 into an orientation in one direction, a large magnetic field in initializing magnetic impression means 8 is necessary.
(3) Preceding the magnetic modulation recording, anticipatory position adjustment has to be performed in order to locate the magnetic field in the focused laser spot effectively.
(4) If the temperature changed after the initialization, or tilt occurred due to humidity variation, then it was difficult to perform recording/reading/erasure with the most suitable operation power.
(5) Based on magnetic field modulation recording, overwriting is of course possible, and in the case of a high density recording, it is a great advantage that the recording power margin is very broad. This is to avoid a condition of neighboring marks resembling overlapping circles, because in magnetic field modulation recording, the recording occurs while the portion of the mark that has just been formed is repolarized. However, if a high density recording is attempted by making the track intervals narrow, then the broad recording power margin turns into a disadvantage. In other words, in the case of magnetic field modulation, even with excess recording power, the recording power is likely to be set on the higher side, in order to prevent the recording marks from turning into an overlapping circles condition. In that case, even though the overlapping circles condition could be avoided, there have been problems such as the enlargement of the recording mark, the deletion of recorded marks in neighboring tracks, or the increase of cross-talk.
(6) Hitherto, in devices for the reading of magneto-optical recordings, during short term stand-by periods for recording or reading, the focus servo and the tracking servo were operating and standing by under reading conditions. However, if the servos have to stand by under reading conditions in a magnetic super resolution type magneto-optical recording medium, which necessitates a reading magnetic field, there has been the problem of waste through dissipation of power in the electromagnet type magnetic head.